1. Technical Field of the Invention
The present invention relates to a male screwthread that is configured in such a manner that loosening and return are prevented (self-locking) when the screwthread is engaged with a female screwthread.
2. Related Technical Information
As shown in FIG. 3, a male screwthread 1 and a female screwthread 2 conforming to metric screw regulations used in the conventional art are each formed to have a thread angle of 60 degrees, distributed symmetrically with a half-angle of 30 degrees with respect to a plane perpendicular to the axis thereof. One known method (self-locking) of preventing loosening and return is to ensure that deformation occurs in a plurality of thread ridges of the female screwthread, to provide buffer-zones between the female screwthread and the male screwthread.
However, when a tightening load is applied to male and female threads conforming to the metric screw regulations, elastic deformation of the thread ridges of the male screwthread is greater than elastic deformation of the thread ridges of the female screwthread, so that the surface pressures generated in both the flank surfaces subjected to the load are not even. When the flank surfaces of the thus configured male and female screwthreads deform elastically in contact with one another, the center of action of the load is biased towards the root sides thereof. This reduces the torque radius, giving rise to a problem in that it becomes easy for loosening to occur between the male or female screwthread and the other screwthread. Deformation of the thread ridge of the female screwthread leads difficulties in manufacture, which causes problems involving increased costs.
The present invention was devised in the light of the above problem, with the objective of providing a male screwthread that does not cause loosening or return (self-locking) when engaged.